I have an SE34I.2 which I run into Omega Loudspeakers 97dB-efficient Hoyt-Bedfords. Volume-wise, I am not having any issues; it is more than enough. However, I am not happy with the bass response in general.

In front of the SE34I.2, I have a CSP preamp. I have tried both 6922's and 6N1P's on the pre. Before the CSP, I have a Hegel HD20 DAC and a Mac Mini as the source.

On the SE34I.2, I have tried both Mullard NOS GZ32's and some Raytheon and Sylvania 5U4GB's. As far as the output tubes, I have tried the stock Mullard EL34's and the fat bottle EH 6CA7's. I am using 6N1P's for input tubes.

What else would you recommend for improving the bass response? Which of the tubes (input, output, and rectifier) have the most effect on the bass?

Well, it seems to me that you should be getting pretty good bass on the Integrated as is. Have you tried 6N2P tubes at input? They sacrifice some headroom, but give a very warm sound and more bass in my experience. Also. . .how are your amps situated? I found hidden bass in my setup when I moved to using Herbie Audio Labs' "IsoCups"--these improve all aspects of the sound on my amps for me, including giving me a better defined, more audible bass spectrum.

Thanks for the quick response. I have not tried the 6n2p's in my system. I remember using them in my SE84s and being very happy, but when I sold them, the tubes went as well. I will definitely give them a try next time I can have a hand on them.

I will definitely look into the IsoCups; actually this is the first time I have heard about them.

Here's another vote for the Herbie's Iso-Cups. I have those, their Tenderfeet, and the MIGs. Overall, the best results for me have been the Iso-Cups under my Toriis and Ultra, then the SE84ZS and Taboo (headphone amp only, so less microphonics and feedback). But I also got much clearer, tighter bass out of my ERRs with the screw-in dampener/slider feet. On my source boxes, all the devices help, and the differences between them are less obvious.

Not to dissuade you from shopping Herbies or trying different tubes, but it seems that the more direct way to address your problem is with speaker placement. Have you tried relocating them closer to room boundries, i.e. closer to the back wall? That would yield several db gain in the bass, and as a bonus, it's free!

I am not sure that Alper said he wanted a gain in bass. If he does, then sure, speaker placement should be able to raise or lower bass reinforcement. And you're right, it's free. But that's not the same as good bass.

Proper speaker placement is always the right place to start, but once you have that box checked off, I think you have to start asking yourself how deep you might want to go into bass management. Room treatment can be a huge factor, but effective bass traps might not be an option.

I followed a series of articles recently that convinced me I needed to start actually measuring bass response in order to understand the macro factors of the room, size and contents. Then, build (read "have built"; I am no carpenter) servo subs roughly to meet the needs of the room, then break all that in, re-measure, adjust the subs and their amps, and then start playing with tubes.

FWIW, I love the ERR bass. It is amazingly good for a speaker of its modest footprint. It is more than satisfying, but few speakers can do the full 20-20 as well as a sub-integrated system.

Let's get real here. No amount of tube rolling or isolation devices will provide more power, extension, or alter damping characteristics from an SE34i, nor change the inherent qualities of the OP's Omega speakers, and those are the limiting factors for his system's bass response.

Maybe the impedance load in the bass region that the Omegas present is less than ideal for power delivery from the SE34. I know my little Zens like low impedance speakers, and if the SE34 has the same output trannys using the same taps, it's no wonder the results with a >8ohm load like the Omegas are less than spectatular. If that's the case, and I could be wrong, the OP would be better served having Steve install the higher load friendly EX trannys or using an autoformer to cut his impedance in half than spending money on tubes and damping devices.

I think more assessment of the problem is in order, as Alper only said he is "not happy with the bass response in general", which could mean just about anything.

I have not played much with the placing of the speakers, but I think I am benefiting from some mechanical coupling as they are currently located closer to the wall, but I need to experiment more with it.

Unfortunately, I do not know the impedance curve of the speakers at bass frequencies. I know that the vented freq is from 38hz to 18khz and they are 8 ohms, but I do not have more information other than what is provided on the Hoyt-Bedford website.

What I mean by "not being content with the bass response" is simply based on my experience with my Torii mkII, which has very good bass even with inefficient speakers at 91dB and complex crossovers. I know that SET amps are known for their spectacular mids and highs, and because of the resolution of the amp and the speakers, every single detail including the bass is heard fine, but the system sounds a bit imbalanced, less pronounced in bass, and much more present in mids and highs.

Sounds like you've found the SE34's Achilles heelReply #12 - 01/03/12 at 18:36:05

I think I know what you're hearing. Bear with me here, long post...Torii II to SE34 is a big clue.

Listen carefully in the bass. You mentioned the slightly prominent midrange relative to the bass. Do kick drums seem to have extra impact, punch, or presence, with otherwise laid back bass response?

Does this describe what you're hearing?

If so, you could be experiencing the effects of higher output impedance than you're used to. With the lower damping factor of the SE34i I would expect the bass response to be slightly reduced (maybe a couple db) compared to the midrange, and a couple small but notable peaks (that crest at levels near that of the midrange) that correspond to the cone's resonant freq and the port's resonant freq. This is the fairly typical way high output impedance amps behave with ported/reflex enclosures. This stands even if the power delivery from the SE34i to the Omegas is ideal.

The port resonance point should not be too much concern, as the speaker is likely rolling off by that point, so it will tend to extend the reponse you get. The woofer resonance is probably an octave or so higher, and non-linearity will be more noticable (for example, extra presence on kick drums for would be a peak somewhere from 70-100hz).

On my speakers, which I can reasonably presume present a much wilder load as far as impedance/phase goes, the deviation from linearity is still only about +/-2.5db (as measured at the speaker terminals with amp connected). I actually have a jpg of that, if I could figure out how to attach it here, it would go further than my convoluted explanation.

I would expect a more SET-friendly purist speaker like your omegas would have much less deviation than what I use, but the non-linearity is the nature of the beast with the higher output impedance. To cure it would require applying negative feedback, and possibly more gain stages or other complexity in the amp, which would rob it of it's uber clarity/transparency.

You also noted something I have also observed, that the SET detail and tone is all there in the lower registers, even if the response is slightly attenuated and a little lumpy/peaky. That's the rub. The detail and tone is addictive, and you don't want to do without it.

One thing you may consider doing which would preserve all the SET goodness and directly help cure your bass is simply adding a decent sub. Feed it speaker level inputs so it get's the Decware sonic signature. You'll extend your response much deeper, and smooth out and firm up the midbass at the same time.

Check out Rhythmic for high value, high performance, well damped ('fast' sounding) subs that can keep up with your Omegas. I think their 15" sealed job is going for only $500 right now.

For what its worth.....I once heard an SE34I with the four EL34 tubes that had KT77's installed. The difference in bass from the EL34 to the KT77 was outstanding while still keeping what the EL34 did so well. The KT77 worked real well in my first Generation Torii, giving the same effect.

I have no idea if the same results could be had with the SE34-2 or not, but for the price of two tubes, it might just be worth it.

You have translated what I have been hearing into words so well. As soon as the break-in is completed (I still have 200-250 hours to go), I will start investigating all the options you have presented, namely the EX mode as well as the sub-bass enhancement.

I took the advice by Ski Bum and went for a active subwoofer by Dali. It is the IKON SUB MK2 model and it has improved the system significantly.

I was not so sure about swapping the EL34's with KT77's as that would be giving up the benefits from the Hazen Grid Mod which I like. Also, I went back to my NOS Mullard GZ32's which can be slightly bass shy in comparison to the Sylvania's I had (this might be a pseudo effect that I think I am hearing though). So, I went back to my favorite set of tubes with this amp.

Anyway, to cut the long story short, I am currently a happy camper! Thanks for all the input!

I recently bought a pair of Genalex Gold Lion KT77's just to give a try... It has some serious bass in comparison to the EL34's. So the current tube combination is as follows:

On the SE34I.2+:6N1P (bought from Decware)Genalex Gold Lion KT77GZ32 (Mullard NOS from 1967)

On the CSP:6N2P on all three positions (bought from Decware)Bendix 6106

Lon - I tried the 6N2P's on the SE34 further to your reccommendation, but they were a little on the loud side as far as hum goes. Without the pre in the signal chain, that amp is dead silent with all sorts of tubes. Somehow, as soon as the CSP is put in lime, there is hum in the system, which is fine with 6N1P on the SE34, but when I swap them with the 6N2P's, somehow, it gets quite loud. Not as loud as getting in the way of the music, but when nothing plays...

Sorry about the hum on the .2 with the 6N2Ps. I did finally find two to use in that amp that were low enough in hum that I could use them. . . . Most however had big hum issues.

I haven't tried KT77s in a long time, although they made impressive bass I couldn't get past their treble presentation at the time. But that was before I had amps with Steve's treble cut circuit. . . . .